The present invention relates to a process for preparation of substituted aromatic compounds that are useful as products or intermediates for industrial chemicals, polymers, medical and agricultural chemicals and others, using halogenated aromatic compounds, especially chlorinated aromatic compounds that are industrially producible and available at a low price as starting materials and by substituting the chlorine atom of the above described chlorinated compounds with various nucleophilic substances.
As one method for producing substituted aromatic compounds, a nucleophilic substitution reaction of aromatics is known in which a halogenated aromatic compound is reacted with a nucleophilic agent to substitute the above described halogen atom with the nucleophilic species, but it is also known that generally a halogenated aromatic compound has remarkably low reactivity to a nucleophilic species as compared to a aliphatic halogenated compound. However, if a specific substituent exists at a specific position of an aromatic ring as in p-nitrochlorobenzene, 2,4-dinitrochlorobenzene, or p-benzoylchlorobenzene (active halogenated aromatic compounds), the halogen atoms of the halogenated aromatic compounds is remarkably activated to the nucleophilic substitution reaction by the substituent to progress easily the reaction.
On the other hand, as described in xe2x80x9cOrganic Chemistry (the last volume, Japanese version)xe2x80x9d, 5th edition, written by R. T. Morrison and R. N. Boyd, page 1289 that xe2x80x9cit will end in failure even if a halogenated aryl compound (this is an inactive halogenated aromatic compound in the present invention) or a halogenated vinyl compound is tried to be treated with a usual nucleophilic reaction agent to convert phenol, ether, amine or nitrilexe2x80x9d, it is described each in the following literatures that an inactive halogenated aromatic compound, such as chlorobenzene, p-bromobenzene, o-methoxyiodobenzene or the like, in which no such a substituent exists does not react with a nucleophilic agent unless {circle around (1)} the reaction is carried out in very severe reaction conditions, or {circle around (2)} once the halogen atom in the halogenated compound is activated by making it an organic metal complex in which the aromatic ring is a ligand, or {circle around (3)} a catalyst is made to exist: {circle around (1)} Fyfe, in Patai, xe2x80x9cThe Chemistry of the Hydroxy Group,xe2x80x9d pt.1, pp.83-124, Interscience Publishers, Inc., New York, 1971; {circle around (2)} Semmelhack and Hall, J. Am. Chem. Soc., 96, 7091, 7092 (1974); M. Fukui, Y. Endo and T. Oishi, Chem. Pharm. Bull., 28, 3639 (1980); or {circle around (3)} A. A. Moroz and M. S. Shvartsberg, Russ. Chem. Rev. 43, 679-689 (1974); Mowry, Chem. Rev., 42, 189-283 (1948), pp207-209; S. L. Buchwald et al., J. Am. Chem. Soc., 119, 10539-10540 (1997); S. L. Buchwald et al., J. Am. Chem. Soc., 122, 1360-1370 (2000).
Among inactive halogenated aromatic compounds, in particular, chlorinated aromatic compounds have extremely low reactivity as compared to corresponding halogenated aromatic compounds of non-chlorinated series and no effective reaction agent or catalyst have been available. However, because the above described chlorinated compounds are industrially producible and available at a low price, recently, various kinds of reaction agents and catalysts have been developed to achieve the nucleophilic substitution reaction of inactive chlorinated aromatic compounds. For example, in L. I. Goryunov and V. D. Shteingarts, Russ. J. Org. Chem., 29, 1849-1855 (1993), it is disclosed that using Rh complex, which is expensive and difficult to be industrially produced, as a catalyst and chlorobenzene as a raw material, methoxybenzene can be obtained in the yield of 60 to 75% by reacting the chlorobenzene at reaction temperature between 80xc2x0 C. and 180xc2x0 C. for 4 days to 1 hour. In U.S. Pat. No. 5,315,043 or U.S. Pat. No. 6,087,543, it is disclosed that a specific fluorination reagent are reacted with chlorobenzene under very severe conditions of at a temperature between 210xc2x0 C. and 450xc2x0 C. to produce fluorobenzene in the yield of 6 to 70%.
An object of the present invention is to provide an effective method to produce substituted aromatic compounds from halogenated aromatic compounds, especially chlorinated aromatic compounds, with high yield under mild reaction conditions by using reaction reagents which are extremely effective to the nucleophilic substitution reaction.
Accordingly, the present invention is a process for preparation of a substituted aromatic compound substituted with Q, which comprises:
reacting a phosphazenium compound represented by formula (1) 
xe2x80x83(in the formula, Qxe2x88x92 represents an anion in a form derived by elimination of a proton from an inorganic acid, or an active hydrogen compound having an active hydrogen on an oxygen atom, a nitrogen atom or a sulfur atom; a, b, c and d, each independently, is 0 or 1, but all of them are not 0 simultaneously; and R groups represent the same or different hydrocarbon groups having 1 to 10 carbon atoms, or two Rs on each common nitrogen atom may be bonded together to form a ring structure) with a halogenated aromatic compound having halogen atoms; whereby, at least one halogen atom in the halogenated aromatic compound is substituted with Q (where, Q represents an inorganic group or an organic group in a form derived by elimination of one electron from Q in formula (1)).
The present inventors have earnestly studied for the purpose of providing a method of industrially favorably producing substituted aromatic compounds, resulting in finding that the reactivity of various nucleophilic anion species represented by Qxe2x88x92 in formula (1) to the nucleophilic substitution reaction of aromatics is drastically improved by the use of a phosphazenium cation in formula (1) as a counter cation. The inventors found that with the use of phosphazenium compounds represented by formula (1), the nucleophilic substitution reaction of inactive halogenated aromatic compounds, especially inactive chlorinated aromatic compounds, which had been conventionally considered to be difficult, could be progressed under extremely mild conditions and objective substituted aromatic compounds could be obtained in high yields. As a result, the present invention is completed.
To be concrete, for example, as shown in Example 1 and Example 2 to be described later, it has been found surprisingly that tetrakis[tris(dimethylamino)phosphoranylideneamino]phosphonium methoxide: [(Me2N)3Pxe2x95x90N]4P+, MeOxe2x88x92 (Me represents methyl group in the formula and the following description) easily reacts with chlorobenzene at room temperature to produce desired methoxybenzene in the yield of 95%, and that when tetrakis[tris(dimethylamino)phosphoranylideneamino]phosphonium fluoride: [(Me2N)3Pxe2x95x90N]4P+, Fxe2x88x92 is used, it reacts with chlorobenzene under an extremely mild condition of 130xc2x0 C. compared to the conventional condition to produce fluorobenzene in the yield of 81%.
Further, in one aspect of the present invention, when a substitution reaction with Qxe2x88x92 is carried out, a phosphazenium compound represented by formula (2) 
(in the formula, Zxe2x88x92 is a halogen anion, and a, b, c, d and R groups are the same meaning as described above) and a metal compound represented by MQn (in the formula, M represents an alkaline metal atom, an alkaline earth metal atom, or a rare earth metal atom, Q is the same meaning as described above, and n is an integer from 1 to 3) are used as raw materials and made contact with each other to produce a phosphazenium compound represented by the above described formula (1) in the reaction system, and thus the above described substitution reaction can be carried out.